node: turn overflow_hidden() in a method of the trait

Instead of a RsvgNode method called by trait implementation,
add a method to the trait and call it from the common code.
7 jobs for node in 54 minutes and 21 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #302295
fedora test

00:07:39

 
  Lint
manual #302297
allowed to fail manual
clippy
manual #302296
allowed to fail manual
rustfmt
passed #302298
tarball

00:21:23

 
  Cross Distro
passed #302301
debian_i386:testing

00:25:17

passed #302300
allowed to fail
debian:testing

00:17:35

passed #302299
allowed to fail
fedora:rawhide

00:17:50